[Taxacom] Read... and believe...

Stephen Thorpe s.thorpe at auckland.ac.nz
Fri Sep 4 21:08:59 CDT 2009

Hi Jim,

One thing I do know a thing or two about is diagnostics/identification, and what an identification "means". I have much practical experience and understanding of this area, because it is what I do (and have done nothing else for the last 10+ years). I have to laugh when I read things like the quote from Roger Hyam:

If a specimen is named but the taxonomic classification used in the naming is not specified then it can’t be know which taxon (of the multiple possible taxon
concepts for that name) it has been identified to

Such quotes are way too naively "theoretical"! Taxonomic diagnostics just doesn't work like that in practice! So, how does it work? Let me try to being to suggest how:

(1) An identification without indication of identifier/date is relatively (but not entirely) meaningless, and represents the least desirable situation. Even if an idiot identified something, it is better to know this than to not know the identifier!

(2) Given sufficient experience and familiarity with a group, there is typically a very high level of agreement between competent identifiers on what the taxon boundaries are. The "gaps" between taxa are an empirical feature of the world. Luckily, we do not live in a world where every taxon merges into every other taxon! There are of course some problem cases.

(3) At one stage I had thought of adding the basis for my identification to my identifications, something like:

Examplus primus Smith, 1970, s.d. (=subsequentum descriptionibus =from original description)
Examplus primus Smith, 1970, compared with type
Examplus primus Smith, 1970, keyed in Jones (1980)
Examplus primus Smith, 1970, as identified by Jones, 1975 (unpublished determination label)
Examplus primus Smith, 1970, as identified (anonymously) in NZAC

but it soon became apparent to me that I use a complex combination of things to identify a specimen, and it is not really possible, or necessary, to try to disentangle them all and explicitly state them. Most of the time, there would be no disagreement over the identification - all competent identifiers would agree ...

An identification is a hypothesis, like any other

Very often, there isn't anything that one could call a published taxon concept! There is just a vague original description, and hopefully a type specimen. It is the unpublished taxon concept of the identifier (which is likely to agree in most cases with that of other competent identifiers) which determines the meaning of the identification, which is why we want to know the identifier/date that goes with the identification.

All of this creates a workable system, but perhaps not one that a machine could "understand" ...



From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Jim Croft [jim.croft at gmail.com]
Sent: Saturday, 5 September 2009 5:23 a.m.
To: TaxaCom
Subject: [Taxacom] Read... and believe...

you can weep if you like:

a blog post by Roger Hyam: http://www.hyam.net/blog/archives/598

For example:

" 1. Names are not reliable pointers to taxa. If a specimen is named
but the taxonomic classification used in the naming is not specified
then it can’t be know which taxon (of the multiple possible taxon
concepts for that name) it has been identified to. See Taxa, Taxon
Names and Globally Unique Identifiers in Perspective.
2. Descriptions require human interpretation. As described above, the
use of exemplar specimens combined with descriptions means that
identifications will vary between experts.
3. Relationships between descriptions are vague. The same name may be
used for several separately defined taxa. The descriptions of these
taxa may use the same or different morphological characteristics. Some
descriptions will omit characteristics used in other descriptions that
are ostensibly about of the same taxon. It is therefore not possible
to say whether the two description overlap, are equivalents or do not
intersect at all."



Jim Croft ~ jim.croft at gmail.com ~ +61-2-62509499 ~
... in pursuit of the meaning of leaf ...
... 'All is leaf' ('Alles ist Blatt') - Goethe


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